Apparatus for separating charged particles according to their respective ranges

ABSTRACT

An apparatus for separating charged particles according to their respective energies. The charged particles are decelerated and passed through a long cylindrical electrode having a focusing coil. Since the velocity of the particles differs according to their respective energies, the particles are separated in the electrode and exit the electrode at different times.

United States Patent 1 Koilte [111 3,745,337 [451 July 10,1973

[52] US. CL, ..250/4l.9 TF, 250/49.5 AE, 250/495 PE [51] Int. Cl. H01j39/34 [58] Field of Search 250/419 TF, 49.5 R, 250/495 PE, 49.5 AB

[56] References Cited UNITED STATES PATENTS 3,582,648 6/1971 Anderson250/419 TF BULRCE 7/1957 Hendee 250/419 TF 3/I970 Castaing 250/495 PEOTHER PUBLICATIONS Electron Velocity Micro-Analyzer," Shahbender RCA TNNo. 310, November, 1959.

Primary Examinerlames W. Lawrence Assistant Examiner-C. E. Church IAttorney-Webb, Burden, Robinson & Webb [5 7] ABSTRACT An apparatus forseparating charged particles according to their respective energies. Thecharged particles are decelerated and passed through a long cylindricalelectrode having a focusing coil. Since the velocity of the particlesdiffers according to their respective energies, the particles areseparated in the electrode and exit the electrode at different times.

3 Claims, 8 Drawing Figures 40 4 4 1 33 20 k 6 5 g MAGNETIC FIELDCONTROL CIRCUIT Patented July 10, 1973 4Shecs-Sheet 1 /ZHIGH ,VOLTAGEGENERATOR VOLTAGE SUPPLY 2 46 g a a N m A .F'g J h )4 f l r J5 T YDETECTOR FF 49 D|sPLAY I DEVICE AMPLIFIER b 1 AC Patented July 10, 19733,745,337

4 Sheets-Sheet 2 DETECTOR E 3 I SYNCHROSCOPE a q j j EAMPLIFIER SOURCESOURCE EEIW 33 20 f4 4 3,? 1 I l. wwn w DETECTOR AMPLIFIER 4Sheets-Shoot 1 Zap/H 1 Sheets-Sheet 1 CCC CIFbIillZll :L \r

womnow- APPARATUS FOR SEPARATING CHARGED PARTICLES ACCORDING TO THEIRRESPECTIVE RANGES This invention relates generally 'to an apparatus forseparating charged particles according to their respective energies andmore particularly to an apparatus for separating charged particles whoserespective energies vary with time.

In the usual technique forseparating charged particles, they are causedto traverse either an electric or magnetic field. In either case, thecharged particles traverse the field at a certain velocity and theirtrajectory or flight path varies according to the energy of therespective particles or groups of particles. Particles having therequired energy exit the field via a slit in a baffle which ispositioned so as to intercept the particles having energies greater orless than that required. The particles that would be intercepted arethen made to pass through the slit in sequence either by moving the slitup and down or by varying the intensity of the electric or magneticfield.

In the prior art the energy difference capable of separation (i.e.,resolution) has been limited to about l mev. The resolution iscontrolled by the characteristics of the electric or magnetic field andthe width of the slit.

In the present invention, the velocity of the charged particles isreduced and the retarded or decelerated particles are passed through along cylindrical electrode. As the velocity of the particles differsaccording to their respective energies, the particles are spatiallyseparated along their path in the electrode and, therefore, exit theelectrode at different times. In this way, the energy difference capableof separation is reduced below mev.

It is an advantage of apparatus according to this invention that theyare capable of precisely separating charged particles according to theirrespective energies. It is another advantage that they are capable ofseparating charged particles according to their respective energiesdependent upon time.

Various other objects and advantages of this invention will becomeapparent from the following detailed description read in conjunctionwith the drawings in which:

FIG. 1 shows an embodiment of this invention in which electrons areseparated according to their respective energies;

FIG. 2 shows the wave forms of the voltages supplied to the deflectingmeans in the embodiment shown in FIG. 8 shows the deflecting voltage anddistributions of the particles passed through the slits in the modifiedembodiment shown in FIG. 7.

Referring to FIG. I, an electron beam is produced by an electron guncomprising a cathode l, a Wehnelt electrode 2 and an anode 3. TheWehnelt electrode 2 is connected to the negative terminal of a highvoltage generator 4 and to the cathode 1 via a bias resistor 5. By sodoing, the electron beam current is maintained at a constant value. Theelectron beam, after passing through the Wehnelt electrode 2, isaccelerated by the anode 3 which is grounded and then enters a firstcylindrical electrode 6, also grounded.

An electrostatic or electromagnetic deflecting means l2 and a slit 13are provided in the cylindrical electrode 6 in order to control theelectron beam. The deflecting means may, for example, comprise a pair ofparallel plates charged with opposite polarities or a pair of coilshaving facing ends of opposite polarities. A voltage supply source 16supplies a controlling voltage or current to the deflecting means 12.When a voltage is applied to said deflecting means (e.g., V in FIG. 2a)the electron beam is deflected and intercepted by the baffle 13containing a slit. On the other hand, when the voltage applied to thedeflecting means 12 is zero, the electron beam passes through said slitin the baffle 13 and enters a second cylindrical electrode 8 to which avoltage, approximately the same as the voltage applied to the cathode 1,is supplied by a voltage regulator 11 comprising batteries 9 and avariable resistor 10. By so doing, the electrons constituting theelectron beam are decelerated by a decelerating electric field producedbetween the first and second electrodes and, therefore, pass through thesecond electrode 8 at a reduced velocity. However, since the flow rateor speed of high energy electrons is higher than that of low energyelectrons, the electrons are separated according to their respectiveenergies. Further, in order to produce a uniform magnetic field alongthe center axis of the electrode 8 and, thereby, create a situationwhereby the electrons move along the said axis repetitively andperiodically, said electrode is equipped with a focusing coil 20. As aresult, the energy of the electrons maintain their respective levelsand, hence, their respective velocities. The length of the secondelectrode 8 defining.

an elongate passage through which the decelerated electrons pass isabout 30 cm m.

The electrons, upon reaching the outlet of the electrode 8, areaccelerated by an accelerating electric field produced between saidelectrode 8 and a third electrode 7 which is grounded. An electrostaticor electromagnet deflecting means 14 and a slit 15 are provided in thethird electrode 7 in order to control the ac celerated electrons. Thevoltage supply source 16, as in the case of the deflecting means 12,supplies a controlled voltage to the deflecting means 14. When a voltageapplied to the deflecting means (e.g., V in FIG. 2b) the electrons aredeflected and intercepted by the baffle 15. On the other hand, when thevoltage applied to the deflecting means 14 is zero, the electrons passthrough the slit in baffle 15 and are detected by a detector 17. Thedetected signal is then amplified by an amplifier l8 and fed into arecorder or display means In the above arrangement, the electrons passthrough the slit in baffle l3 and are decelerated by the deceleratingelectric field produced between the first and second electrodes 6 and 8during the period A 1'; that is to say, during the time no voltage isbeing applied to the deflecting means 12. During this period of time,the energy of the decelerated electrons traversing electrode 8 towardsslit 15 is very low, for example, 10 mev. The period 1' during which theelectrons pass from the slit in baffle 13 to the slit in baffle 1.5 isexpressed as follows:

where V is the electron velocity, m is the electron mass, E is theelectron energy and l is the distance between the two slits.

It is apparent from the above equation that 1 varies according to E.When E is large, T is short and conversely, when E is small, 7 is long.Therefore, by making A r extremely short as compared to 1' electronshaving energy (velocity) substantially corresponding to T only passthrough the slit in baffle 15.

Now, if two electrons having energies of E and E I A E respectivelyenter the second electrode 8, the time taken (r 7 for each electron topass from the slit in baffle 13 to the slit in baffle 15 is given asfollows:

Thus, the time differential 'r, 1 can be expressed as follows:

Further, since the time taken for the respective electrons to pass fromthe slit in baffle 13 to the slit in baffle l5 varies, the energydistribution of said electrons is recorded by or displayed on therecorder or display means 19 as a differential loss curve by varying thevoltage supplied to the second electrode 8 or the frequency of thesignal supplied to the deflecting means 12. Still further, by keepingthe voltage and frequency applied to said electrode constant, theapparatus can be used as a monochromater.

FIG. 3 shows another embodiment of the apparatus heretofore described.In the figure, a beam of charged particles emanating from a source 21 isdeflected by a deflecting means 22 so as to scan a slit plate 23provided with a minute opening. Said particles which pass through theopening periodically are directed to a cylindrical electrode 24 similarto the second electrode 8 shown in FIG. 1 and separated according totheir respective energies therein. The separated particles are thenaccelerated by an accelerating electrode 25 and detected by a detector26, the output signal of which is fed into a synchroscope 28 via anamplifier 27. In this embodiment, since there is no deflecting means andslit at the output side of the electrode 24, the separated particles arefree to enter the detector continuously.

The resultant energy distribution curve produced on the synchroscope isshown in FIG. 6.

FIG. 4 shows a further embodiment of this invention. In this case,control electrodes 29 and 30, to which a bias voltage is supplied from acontrol circuit 31, are provided at each end of the long cylindricalelectrode 24. Normally, a bias voltage is applied to both electrodes inorder to intercept the particles, so that it is only during the shortperiods when said bias voltage is zero that the particles pass throughthe electrodes. It is possible to discard electrode 30 as required. Itis also possible to utilize the control electrode of a charge particlesource; e.g., the electron gun Wehnelt electrode in FIG. 1 to which saidbias voltage is applied instead of electrode 29.

FIG. 5 shows yet another embodiment of this invention. In the figure,the charged particles emanating from the source 21 are deflected by thedeflecting coil 22 and scan the slit plate 23 in the same way as in theembodiment shown in FIG. 3. The particles passed through said slit platethen enter a magnetic field 32 (shown as its optical analog) wherein theparticles are directionally changed so as to direct them into anelectrode 33 maintained at ground potential. The particles aredecelerated by a decelerating electric field produced between electrodes33 and 24, thus causing the particles to travel along the cylindricalelectrode 24 at an extremely low velocity. A mirror electrode 34 isplaced at the end of the long cylindrical electrode 24 so that areflecting electric field of the particles is produced in front of saidmirror electrode. The particles reaching the end of the electrode 24 arereflected by said reflecting field and then travel along the electrode24 in the reverse direction. The reflecting particles are accelerated bythe electrode 33, again directionally changed by the magnetic field 32and then detected bp the detector 26. The detected signal is fed viaamplifier 27 into a sampling scope or synchroscope 28 which displays anenergy distribution curve of the separated particles as shown in FIG. 6.

In the above embodiment, since the particles traverse the cylindricalelectrode 24 twice, the effective passage length is doubled. Therefore,the separability of this embodiment is twice as good as the embodimentsshown in FIGS. 1, 3 and 4. It is also possible to place a deflectingmeans and a slit between the magnetic field 32 and the detector 26 so asto detect only one portion of the separated particles.

FIG. 7 shows a modified embodiment of the embodiment shown in FIG. 5. Inthis case, two slits 40 and 41 and a deflecting means 42 to which acontrolled voltage is applied from a control circuit 43 are arranged'between the magnetic field 32 and the electrode 33. An example of saidcontrol voltage'is shown in FIG. 8a. When the voltage is zero; namely,at time 1- the particles pass through both slits. FIG. 8b shows thedistribution of the particles passed through the slits. Said particlesare decelerated by the decelerating field produced between electrodes 33and 24, thereby traveling along electrode 24 at a very low velocity. Theparticles reaching the end of said electrode are reflected in thereverse direction by the mirror electrode 34. The reflecting particlesare accelerated by the electric field produced between electrodes 24 and33, pass through slit 41 and are then directed to the deflecting means42.

FIG. 8c shows the distribution of the particles that would pass throughthe slit 41. At time 1- namely, when the voltage supplied to thedeflecting means is zero, the particles pass through the deflectingmeans and the slit 40 without being deflected. FIG. 8d shows thedistribution of the separated particles passed through the slit 40. Theseparated particles are directed to the detector by the magnetic field.In this arrangement, particles having the desired energy are detected bycontrolling a periodic time 2 1- of the voltage supplied from thecircuit 43 to the deflecting means. When the accelerating voltage of thesource 21 is varied continuously and the periodic time 2 T is fixed, thedifferential loss curve similar to FIG. 6 is obtained.

Further, if the frequency of the rectangular pulse supplied to thedeflecting means 42 is varied, the differential loss curve as shown inFIG. 80 is obtained.

Having thus described my invention with the detail and particularity asrequired by the Patent Laws, what is desired protected by Letters Patentis set forth in the following claims.

I claim:

1. An apparatus for separating charged particles according to theirrespective energies comprising:

a. means for decelerating said particles;

b. an enclosure defining an elongate passage through which saiddecelerated particles pass and in which said particles are separatedaccording to their respective energies;

c. a magnetic field for deflecting and directing unseparated chargedparticles into one end of said passage, said field also deflecting theseparated particles emerging from said end; i

d. a reflecting means for reflecting the charged particles, saidreflecting means being provided at the second end of said passage;

e. a control means for directing said particles into said passage viasaid magnetic field during a very short period of time; and, V

f. means synchronized with said control means for detecting theseparated particles.

2. An apparatus for separating charged particles according to theirrespective energies comprising:

a. means for decelerating said particles;

b. an enclosure defining an elongate passage through which the saiddecelerated particles pass and in which said particles are separatedaccording to their respective energies;

c. a magnetic field for deflecting and directing unseparated chargedparticles into one end of said passage, said field also deflecting theseparated particles;

d. a reflecting means for reflecting the charged particles, saidreflecting means being provided at the second end of said passage;

e. first and second spaced baffles having slits therein provided betweensaid magnetic field and said passage;

f. a deflecting means provided between the baffles for deflecting thecharged particles, said particles directed into said passage beingcontrolled by said deflecting means and the second baffle, the chargedparticles separated in said passage being controlled by said deflectingmeans and the first baffle; and,

g. control means for causing the deflecting means to pass unseparatedparticles through beffles for a short interval and at a measured timelater to pass separated particles through said baffles.

3. An apparatus according to claim 2 wherein said enclosure comprises along cylindrical electrode having a focusing coil thereabout.

1. An apparatus for separating charged particles according to theirrespective energies comprising: a. means for decelerating saidparticles; b. an enclosure defining an elongate passage through whichsaid decelerated particles pass and in which said particles areseparated according to their respective energies; c. a magnetic fieldfor deflecting and directing unseparated charged particles into one endof said passage, said field also deflecting the separated particlesemerging from said end; d. a reflecting means for reflecting the chargedparticles, said reflecting means being provided at the second end ofsaid passage; e. a control means for directing said particles into saidpassage via said magnetic field during a very short period of time; and,f. means synchronized with said control means for detecting theseparated particles.
 2. An apparatus for separating charged particlesaccording to their respective energies comprising: a. means fordecelerating said particles; b. an enclosure defining an elongatepassage through which the said decelerated particles pass and in whichsaid particles are separated according to their respective energies; c.a magnetic field for deflecting and directing unseparated chargedparticles into one end of said passage, said field also deflecting theseparated particles; d. a reflecting means for reflecting the chargedparticles, said reflecting means being provided at the second end ofsaid passage; e. first and second spaced baffles having slits thereinprovided between said magnetic field and said passage; f. a deflectingmeans provided between the baffles for deflecting the charged particles,said particles directed into said passage being controlled by saiddeflecting means and the second baffle, the charged particles separatedin said passage being controlled by said deflecting means and tbe firstbaffle; and, g. control means for causing the deflecting means to passunseparated particles through beffles for a short interval and at ameasured time later to pass separated particles through said baffles. 3.An apparatus according to claim 2 wherein said enclosure comprises along cylindrical electrode having a focusing coil thereabout.